Thursday, June 28, 2012

Transmitter FM 45W with valve

TECHNICAL CHARACTERISTICS:
Tendency of catering: 220V AC
Frequency of emission at FM: 88~108MHz
Force of expense: max 45W (without the R3),

Materially:
R1 15KW/2W
R2 1KW/10W
R3 1KW/10W (for biggest force in the exit you replace with short-circuit).
C1 50pF trimmer
C2 30pF trimmer
C3 22pF/4KV
C4, c6, c9 10nF/1KV
C5, c7 1nF/1KV
C8 100mF 100mF/450V (Double electrolytic)
C9, c10 10nF
RFC1, rfc2, rfc3 air Inductors: 15 coils diameter 8mm, from wire 1mm.
T1 Transformer 220V/6V-1A
T2 Transformer of configuration with being first 4 or 8W
T3 Inductor with core ferrite (externally it resembles with small transformer but has a turn only).
D1 BY127 rectifier
Lamp 807 SYLV USA or EL34 or equivalent
ANTENNA Simple dipole L/2. (L= wave length)
S1 Main switch of catering.
S2 Switch of catering of rise (him we close after zestacej' the thread).
Most elements you can him find in a old back-white television with lamps.
Regulations:
With the C2 we regulate the frequency.
With the C1 we adapt the resistance of aerial (practically him we regulate so that it is heard our voice in the radio as long as you become cleaner).
Notes:
The catering better it does not become at straight line from the network 220V but via transformer 220V/220V of isolation and safety 1A.
When does not exist the R3, the force of expense is bigger, but respectively is increased also the hum 50Hz, because the simplicity of designing.
The control (Audio In) can become from a kasseto'fwno or other powerful source. If it is microphone it will be supposed precedes amplifier so that it acquires a force of order of 8W roughly.

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Nostalgic Crystal Radio

It was the first circuit i started with, and it can be build with really junk items. Apart from the diode (which replacement would need a PbS, Lead Sulphyde, galena cristal) everything you can see in the circuit (for the no power version) can be built with enamel wire, alluminium cooking foil, carton wax and so on. The real painful part is to find a high impedance headphone, it is unlikely yo find one at present day but it is possible. In addition I substituted an high internal impedance headphone with a opamp and normal
headphone but doing so you need power. Anyway if you are lucky you can find such a headphone.
Circuit diagram:
Operating Principle:
The AM signal is captured by the antenna , 10 mt long horizontal wire, WELL insulated from earth (I mean distant, to lower the stray capacitance coupling with ground which will adsorb some signal ). The Inductor and capacitor forms a resonator, that will tune with the station which frequency is F= 1/ (2*pi*sqrt(L*C)), so adjust C1 for tuning. The signal is rectified (demodulated) and smoothed by C2. The high impedance headphones has fine internal wiring and lots of windings, so even a small current will produce an audio output.
Construction of components:
Antenna:
10 mt of electrical wire, WELL insulated from ground (use plastic bottle caps and hoowup wire to keep it high). This must be the arrangement |=wall ..=hookup wire o=plastic cap --=wire antenna :
| 10 mt |
wall |...O...O...O----------------------------------O...O...O...| wall
| | |
to receiver
Inductor:
wind 60 windings of enamel copper wire onto a 2 inch ferrite core (1 cm diameter or a bit less)
RF GROUND:
Like for tesla coils, it must be a good ground, otherwire the signal will be poor. Place a metal nail and connect to the circuit with alligator clips.
C1:
It would be difficult to make it reliable, in addition needs a capacitance meter, better buing it or finding it in old broken radios.
But if you want to build it use the parallel plate capacitance formula and make two carton disks (10 cm diameter with a alu foil semi disk each separated through paper, place a nail in center (make sure to not short the capacitor) and connect it with small wires, rotating a disk respect to the other will change shared surface and increase capacitance, but how i said this is not reliable because as soon ase you approach it, you will detune it. So better use a commercial variable cap with insulated lever.
C2:
use paper, alu foil or ldpe (but i don't think that you will be interested in a 10KV capacitor so use thin LDPE)
Diode:
Buy it. I don't advice you looking for Lead Sulphyde cristals....
High impedance headphones: Difficult to find , the only substitute is an amplifier (see below)
Amplifier low impedance headphones: Use a general purpose opamp with feedback resistors and a low impedance headphone (as these of cassette, cd players), but you need power... :-(
It is very nice to build, hearing a sound of a radio station without power is very fun. I reconstrected it basing on my fathers rememberings and very old texts, improved a bit with some physics. Constructing from almost anything is possible , even the headphone, as many cristal radios have been found in nazis prison camps build by prisoners from very limited resources (as everything in a prison camp) and some in foxholes (called foxhole radios).
Anyway, as i ever say, learn and have fun
Source: http://www.hqew.net/circuit-diagram/Nostalgic-Crystal-Radio_5152.html

Doorbell for the Deaf

Description:
This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.
Circuit diagram
Notes:
The circuit uses standard 2 wire doorbell cable or loudspeaker wire. In parallel with the doorbell switch, S1, is a 1N4001 diode and a 12 volt 60mA bulb. The bulb is optional, it may be useful for anyone who is slow to answer the door, all you need to do is flick a switch inside the house, and the bulb will illuminate a label saying Please Wait inside the doorbell switch or close to it. The double pole double throw switch sends the doorbell supply to the lamp, the 22 ohm resistor is there to reduce current flow, should the doorbell switch, S1 be pressed while the lamp is on. The resistor needs to be rated 10 watts, the 0.5 Amp fuse protects against short circuits.
When S2 is in the up position (shown as brown contacts), this will illuminate the remote doorbell lamp. When down, (blue contacts) this is the normal position and will illuminate the lamp inside the house. Switch S1 will then charge the 47u capacitor and operate the transistor which lights the lamp. As a door bell switch is only pressed momentarily, then the charge on the capacitor decays slowly, resulting in the lamp being left on for several seconds. If a longer period is needed then the capacitor may be increased in value.

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Wednesday, June 27, 2012

Combinational Conjuring Trick

Circuit diagram
The simple circuit of Fig.1 emulates a similar conjuring trick which sells for hundreds of Pounds. The trick seems to do the almost-impossible from an electronic point of view, let alone from the point of view of common sense.
It consists of a bank of three on-off switches (S19-S21), which have three switch covers, each of a different colour. These switch a bank of three lightbulbs (LP1-LP3), each of a different colour. The colours of the lightbulbs correspond with the colours of the switch covers.
Now comes the interesting part. The switch covers may be exchanged at will, but still they switch the lightbulbs of corresponding colour. Similarly, the lightbulbs may be exchanged at will, but still they respond to the switches of corresponding colour. On the surface of it, there would seem to be 64 possible connections between switches and lighbulbs, and no possible way that the conjurer can manipulate them all.
However, add some sleight-of-hand, and things become a lot simpler. Each switch cover is symmetrical, in such a way that it looks the same whether facing N, E, or W. Further, each lightbulb is screwed into a circular base, which looks the same whether facing N, E, or W.
Let us consider just one of the switch covers (S19). Three reed switches (S10-S12) are positioned beneath the cover, at positions N, E, and W, and each of these activates a different lightbulb. Any one of the three reed switches may be closed by a single magnet positioned strategically under the switch cover. Depending on the orientation of the switch cover, therefore, the switch will activate any one of the three reed switches, and thus the selected lightbulb.
On discussing this with an accomplished magician, the author was told that this alone would be sufficient for the full effect described - reed switches S1-S9 may be omitted. Nevertheless, the lightbulbs may similarly be surrounded with three reed switches each, which are activated by the orientation of the circular base - a magnet being strategically positioned within it. These reed switches may thus reroute the power to the conjurer's selected lightbulb.
There is just one caveat from an electronic point of view. Carefully consider the voltage and power ratings of the reed switches and on-off switches, to match these with the chosen lightbulbs. Failing this, your trick may demonstrate how none of the switches will activate none of the lightbulbs.

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Magic Wand Conjuring Trick

The simple conjuring trick in Figure 1 is intended to provide some enjoyment for the beginner in electronics or conjuring, and should take only an hour or two to build.
Circuit diagram
The trick works as follows: a wand (with a magnet mounted in one end) must pass in a 1-2-3 sequence over reed switches S4 to S6 before the bulb LP1 will light. If the wand passes over reed switches S1, S2, or S3, the 1-2-3 sequence will be reset (that is, cancelled). Or, if the bulb is already burning, the activation of reed switches S1, S2, or S3 will extinguish it.
All the reed switches - S1 to S6 - are glued just beneath the surface of a 10 cm² box (Figure 2). A general purpose adhesive is suggested, so that the reed switches may later be moved if necessary. The bulb, LP1, is mounted in the centre of the box. A small PP3 9V battery may be used. The prototype box was built using balsa wood.
The wand may be waved back and forth in various motions over the box, on condition that it finally passes in the correct 1-2-3 sequence over S4 to S6 (at which point LP1 will light). This should thoroughly confuse any onlooker and make it virtually impossible for another person to repeat the correct motions with the same wand. The wand may also be lifted just high enough over reed switches S1 to S3 so as not to trigger them.
A 7.2V filament bulb, LP1, was used - instead of, say, a LED - so as not to give the trick an "electronic" appearance.
The operation of the circuit is fairly simple. Three AND logic gates of a 4081 CMOS IC are employed, with gates IC1a to IC1c being configured as a standard cascaded latch circuit. S1 to S3 serve as reset switches. The output at pin 10 will only switch to logic high when reed switches S4 to S6 are closed in sequence. Power transistor TR1 amplifies the output current to light bulb LP1.
Instead of a wand, a small neobdymium (super-strength) magnet may be stuck to one finger, and one's finger used in place of the wand.
In "stand-by" mode (with the bulb extinguished) the circuit will use very little current. Therefore a switch is not included in the circuit (of course, one may be added). The box may be opened and the battery simply clipped on or off.

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Brightness Control for small Lamps

Switching operated 1.5V bulbs
Portable unit, 3V battery supply
Circuit diagram
Parts:
P1 470K Linear Potentiometer
R1 10K 1/4W Resistor
R2 47K 1/4W Resistor (See Notes)
R3 1K5 1/4W Resistor
C1 22nF 63V Polyester Capacitor
C2 100?F 25V Electrolytic Capacitor
D1,D2 1N4148 75V 150mA Diodes
IC1 7555 or TS555CN CMos Timer IC
Q1 BD681 100V 4A NPN Darlington Transistor
LP1 1.5V 200mA Bulb (See Notes)
SW1 SPST Switch
B1 3V (Two 1.5V AA or AAA cells in series, etc.)
Circuit operation:
This device was designed on request, to control the light intensity of four filament lamps (i.e. a ring illuminator) for close-up pictures with a digital camera, powered by two AA or AAA batteries. Obviously it can be used in other ways, at anyone's will.
IC1 generates a 150Hz squarewave having a variable duty-cycle. When the cursor of P1 is fully rotated towards D1, the output positive pulses appearing at pin 3 of IC1 are very narrow. Lamp LP1, driven by Q1, is off as the voltage across its leads is too low. When the cursor of P1 is rotated towards R2, the output pulses increase in width, reaching their maximum amplitude when the potentiometer is rotated fully clockwise. In this way the lamp reaches its full brightness.
Notes:
LP1 could be one or more 1.5V bulbs wired in parallel. Maximum total output current allowed is about 1A.
R2 limits the output voltage, measured across LP1 leads, to 1.5V. Its actual value is dependent on the total current drawn by the bulb(s) and should be set at full load in order to obtain about 1.5V across the bulb(s) leads when P1 is rotated fully clockwise.

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Tuesday, June 26, 2012

Simple Servo Tester

Circuit diagram

click here to download schematic in pdf
This is a simple servo tester which will comprehensively test the capabilities of almost any modern servo. It has two pushbuttons, CENTRE and SWEEP and a potentiometer which works as follows:
- CENTRE Does exactly that, centers the servo, afterwards the potentiometer determines position.
- SWEEP Sweeps the servo back and forth at a rate determined by the potentiometer setting.
The PIC uses its internal timer to set up a constant frame duration of 20ms and the on/off ratio is set by the user.
Have Fun
Ed

PCB board (download it below)

suggested panel decal
Parts
R1 = 1K
R2 = 10K
R3 = 82R
R4 = 10K
R5 = 5K potentiometer
C1 = 27pF
C2 = 27pF
C3 = 100nF
D1 = 4,7V zener diode
Q1 = 10MHz crytal
IC1 = PIC12F675
Download assembly code (.asm)
Download PCB in Eagle format (.br )

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Electromagnetic field detector

Circuit diagram
Description:
This lovely circuit is a real gem! Easy to assemble and more sensitive than many commercial devices available. It's based around an LF351 low-noise operational amplifier and a 1mF choke acting as the sensor. Unlike most other simple EMF detectors, this one has a meter output for accurate reading, but alternatively, you can also roughly estimate the frequency of the field by plugging in headphones. It can detect any field from 50Hz to 100kHz, making it highly versatile and a worthwhile addition to any hobbyist's workbench.
Problems:
I just couldn't find any.
Possible uses:
Find out how far electromagnetic fields extend in your room, house, office...
Are you a ghost hunter? Then this is the circuit that you've been waiting for! Since it has been observed that appearance of a ghost tends to disturb the EMF, you can now detect any such changes with this little detector.

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Linear Resistance Meter

Most analogue multimeters are capable of measuring resistance over quite a wide range of values, but are rather inconvenient in use due to the reverse reading scale which is also non-linear. This can also give poor accuracy due to cramping of the scale that occurs at the high value end of each range. This resistance meter has 5 ranges and it has a forward reading linear scale on each range.The full-scale values of the 5 ranges are 1K, 10K, 100K, 1M &10M respectively and the unit is therefore capable of reasonably accurate measurements from a few tens of ohms to ten Megohms.
Circuit diagram
The Circuit
Most linear scale resistance meters including the present design, work on the principle that if a resistance is fed from a constant current source the voltage developed across that resistance is proportional to its value. For example, if a 1K resistor is fed from a 1 mA current source from Ohm?s Law it can be calculated that 1 volt will be developed across the resistor (1000 Ohms divided by 0.001 amps = 1 volt). Using the same current and resistance values of 100 ohms and 10K gives voltages of 0.1volts (100 ohms / 0.001amps = 0.1volts) and 10 volts (10000 ohms / 0.001amps = 10 volts).
Thus the voltage developed across the resistor is indeed proportional to its value, and a voltmeter used to measure this voltage can in fact be calibrated in resistance, and will have the desired forward reading linear scale. One slight complication is that the voltmeter must not take a significant current or this will alter the current fed to the test resistor and impair linearity. It is therefore necessary to use a high impedance voltmeter circuit.
The full circuit diagram of the Linear Resistance Meter is given in Figure 1. The constant current generator is based on IC1a and Q1. R1, D1 and D2 form a simple form a simple voltage regulator circuit, which feeds a potential of just over 1.2 volts to the non-inverting input of IC1a. There is 100% negative feedback from the emitter of Q1 to the inverting input of IC1a so that Q1?s emitter is stabilised at the same potential as IC1a?s non-inverting input. In other words it is stabilised a little over 1.2 volts below the positive supply rail potential. S3a gives 5 switched emitter resistances for Q1, and therefore 5 switched emitter currents. S3b provides 5 reference resistors across T1 & T2 via S2 to set full-scale deflection on each range using VR1.
As the emitter and collector currents of a high gain transistor such as a BC179 device used in the Q1 are virtually identical, this also gives 5 switched collector currents. By having 5 output currents, and the current reduced by a factor of 10 each time S3a is moved one step in a clockwise direction, the 5 required measuring ranges are obtained. R2 to R6 must be close tolerance types to ensure good accuracy on all ranges. The high impedance voltmeter section uses IC1b with 100% negative feedback from the output to the inverting input so that there is unity voltage gain from the non-inverting input to the output. The output of IC1b drives a simple voltmeter circuit using VR1 and M1, and the former is adjusted to give the correct full-scale resistance values.
Read the rest article at http://www.hqew.net/circuit-diagram/Linear-Resistance-Meter_5099.html

Monday, June 25, 2012

Latching Continuity Tester


"This Latching Continuity Tester can help you locate those difficult-to-find intermittent short and opens that other testers always seem to miss. It has been part of my workbench for many years and performs superb. I have solved many intermittend problem with this highly flexible unit."
Latching Continuity TesterA continuity tester is a must on every service bench for testing cables, pcboards, switches, motors, plugs, jacks, relays, and many other kinds of components. But there are times when a simple continuity test doesn't tell the whole story. For example, vibration-induced problems in automobile wiring can be extremely difficult to detect because a short or open is not maintained long enough for a non-latching tester to respond.
This latching continuity tester detects intermittent (and steady state) opens and shorts. The tester will detect and latch on an intermittent condition with a duration of less than a millisecond. In addition, it provides both visual and (defeatable) audio indicators, uses only one inexpensive and easy-to-find IC, and can be built from all new parts for about $35, or less if you have a well-stocked junkbox.

Circuit Elements:
Schmitt Trigger The heart of the circuit is a 4093 quad tow-input NAND Schmitt trigger, one gate of which is shown in Fig. 1-a. The gate functions as shown in Fig. 1-b. Nothing happens until the enable input goes high. When that happens, the output responds to the input as follows.

As long as the input voltage stays between VH and VL, the output stays high. But when the input goes above VH, the output goes low. The output will not go high again until the input goes below VL. That characteristic is what gives the Schmitt trigger its ability to "square-up" a slowly changing input signal. The Schmitt trigger is ideally suited for our application because it is not dependent on edge triggering, and because both slow and fast signals trigger it when either threshold is exceeded.
We use two gates of the 4093 as a combination detector and latch. The gates are cross connected to form an SR (Set-Reset) flip-flop. When pin 12 goes low, pin 11 will go high. That high may be used to enable an LED or other indicator. Switch S1 is used to select whether the tester will provide ouput when it detects an open or a short. In the OPEN position, pin 12 is held low, so the output of the gate is normally high. When the test leads are connected across a short, pin 12 is pulled high, so the output drops low. The circuit works in the converse manner when S1 is in the CLOSED position.
As shown in Fig. 2-a, we use another Schmitt trigger to build a gated astable oscillator. A gated astable oscillator produces output as long as the GATE input is high. Fig. 2-b shows the waveforms that are present at various points in the circuit. When the pin-8 input goes high, pin 10 goes low, and C1 starts discharging through R1. When VC falls below VL, the output of the gate goes high, so C1 starts charging through R1. When VC exceeds VH, the output again drops low. Oscillation continues in that way as long as the gate input remains high. The frequency of oscillation is given by a fairly complex equation that can be simplified, for purposes of approximation, as F = 1 / R1C1.
Putting it all together:
The complete circuit is shown in Fig. 3. In that circuit, IC1-a and IC1-b funtion as the flip-flop/detector. The output of IC1-a is routed through S4, AUDIO. When that switch is closed, IC1-d is enabled and an audio tone will be output by BZ1. The frequency of that tone can vary from 1000Hz to well above the audio range (100KHz), according to the setting of R4. In addition, R4 varies frequency and volume simultaneously, so you can set it for the combination that pleases you best. Originally we used a PM (Permanent Magnet) speaker. Whe the detector has not been tripped, the full power-supply voltage is across the buzzer, but no current is drawn. The reason is that the piezo element is like a capacitor and does not conduct DC current. Whe the circuit is oscillating, the buzzer consumes a current of only about 0.5 milliamp. The output of the flip-flop/detector circuit also drives IC1-c. If S2 is in the AUTO position, the output of IC1-c will automatically reset the flip-flop after a period of two to six seconds, depending on the position of R7. If S2 is in the MANUAL position, the LED will remain lit (and the buzzer will continue buzzing, if S4 is on) until maual RESET switch S3 is pressed
Construction:
Astable OscillatorThe circuit may be built on a piece of perforated construction board or Vero-board, or on a PCB. The PCB is designed to take board-mounted switches, which makes a neat package and eliminates a rat's nest.
Referring to Fig. 4, mount and solder the components in this order: diodes, fixed resistors, IC-sockets, capacitors, variable resistors, and then the pcb mounted switches. The regular ones will work too it just means more wire. Mount the buzzer and the LED last as described below. Trimmer potentiometer R7 is manufactured by Piher (903 Feehanville Drive, Mount Prospect, IL 60056); it has a shaft that extends through the panel. If the Piher pot is unavailable, an alternate is available from Digi-Key (701 Brooks Ave, South, P.O. Box 677, Thief River Falls, MN 56701). The disadvantage of the alternate is that it has no shaft, so it must be adjusted using a miniature screwdriver.
The circuit board is helf approximately 1/2-inch from the cover by the shafts of the switches. The LED and the buzzer should be inserted in the approproate holes in the pcb now. Then install the top cover, and adjust the height of the LEDso that it protrudes through the top cover. Then solder its leads. Attach the buzzer to the top cover, using silicone rubber adhesive (RTV or double side foam tape.
We mounted a pair of banana jacks on the top of our prototype's case, but you could solder the wires directly to the appropriate points on the circuit board, tie strain reliefs in the wires, and then solder alligator clips to the ends of the wires. However, a set of good leads are really all that expensive and it does give the tester more flexible usage as you have the opportunity to use a variety of different leads to suit your purpose.
The nine-volt battery is secured to the side of the case with a clip or use a holder. Your completed pcb should appear as in Fig. 5.

Usage Hints:
Set S1 for short or open depending on the condition to be tested. Then connect the test leads across the circuit to be tested. If an intermittent condition is detected, the LED will illuminate, and the buzzer will sound (if S4 is on). If you don't remove the test leads (assuming if S2 is set for AUTO Reset, the LED will flash and audio will warble at a rate determined by the reset circuit.
It is very important that the test leads make a positive connection with the circuit to be tested. In fact, clips should be used instead of test leads. There are good test leads available for about $15 which are hardened stainless-steel and have sharpened points which were my personal choice. This detector is so sensitive that, when it is initially connected across a long length of parallel wires or traces, it may latch due to capacitance between the wires. As a matter of fact, it happens with my model all the time. Just press the reset switch S3 when that occurs.

Parts
R1 10K
R2,R3 470K
R4 100K potentiometer
R5 Not used
R6 1.8K (1800 ohm)
R7 1M Trim pot
R8 10M
C1 0.1?F, ceramic
C2,C4 0.01?F ceramic
C3 4.7?F, 16V, Elec. .
IC1 4093B Quad Nand Schmitt Trigger (NTE4093B/ECG4093B)
D1,D1 1N914 or 1N4148 (NTE519/ECG519)
LED1 Red, 5mm, High Brightness
BZ1 Piezzo Buzzer
S1 DPDT, miniature toggle, pcb mount
S2,S4,S5 SPDT, miniature toggle, pcb mount
S3 SPST, momentary push, normally open
Additionally: IC socket, plastic case (4.75" x 2.5" 1.5"),
banana jacks, wire, solder, battery clip,couple cold beers

Copyright and Credits:
The original project is copyright ? by Eldon L. Knight (1986). Document updates & modifications, all diagrams, PCB/Layout by Tony van Roon using Paint Shop Pro deLuxe.
Source: http://www.hqew.net/circuit-diagram/Latching-Continuity-Tester_5084.html

Linear Resistance Meter


Most analogue multimeters are capable of measuring resistance over quite a wide range of values, but are rather inconvenient in use due to the reverse reading scale which is also non-linear. This can also give poor accuracy due to cramping of the scale that occurs at the high value end of each range. This resistance meter has 5 ranges and it has a forward reading linear scale on each range.The full-scale values of the 5 ranges are 1K, 10K, 100K, 1M &10M respectively and the unit is therefore capable of reasonably accurate measurements from a few tens of ohms to ten Megohms.
Circuit diagram

The Circuit
Most linear scale resistance meters including the present design, work on the principle that if a resistance is fed from a constant current source the voltage developed across that resistance is proportional to its value. For example, if a 1K resistor is fed from a 1 mA current source from Ohm?s Law it can be calculated that 1 volt will be developed across the resistor (1000 Ohms divided by 0.001 amps = 1 volt). Using the same current and resistance values of 100 ohms and 10K gives voltages of 0.1volts (100 ohms / 0.001amps = 0.1volts) and 10 volts (10000 ohms / 0.001amps = 10 volts).
Thus the voltage developed across the resistor is indeed proportional to its value, and a voltmeter used to measure this voltage can in fact be calibrated in resistance, and will have the desired forward reading linear scale. One slight complication is that the voltmeter must not take a significant current or this will alter the current fed to the test resistor and impair linearity. It is therefore necessary to use a high impedance voltmeter circuit.
The full circuit diagram of the Linear Resistance Meter is given in Figure 1. The constant current generator is based on IC1a and Q1. R1, D1 and D2 form a simple form a simple voltage regulator circuit, which feeds a potential of just over 1.2 volts to the non-inverting input of IC1a. There is 100% negative feedback from the emitter of Q1 to the inverting input of IC1a so that Q1?s emitter is stabilised at the same potential as IC1a?s non-inverting input. In other words it is stabilised a little over 1.2 volts below the positive supply rail potential. S3a gives 5 switched emitter resistances for Q1, and therefore 5 switched emitter currents. S3b provides 5 reference resistors across T1 & T2 via S2 to set full-scale deflection on each range using VR1.
As the emitter and collector currents of a high gain transistor such as a BC179 device used in the Q1 are virtually identical, this also gives 5 switched collector currents. By having 5 output currents, and the current reduced by a factor of 10 each time S3a is moved one step in a clockwise direction, the 5 required measuring ranges are obtained. R2 to R6 must be close tolerance types to ensure good accuracy on all ranges. The high impedance voltmeter section uses IC1b with 100% negative feedback from the output to the inverting input so that there is unity voltage gain from the non-inverting input to the output. The output of IC1b drives a simple voltmeter circuit using VR1 and M1, and the former is adjusted to give the correct full-scale resistance values.
The CA3240E device used for IC1 is a dual op-amp having a MOS input stage and a class A output stage. These enable the device to operate with the inputs and outputs right down to the negative supply rail voltage. This is a very helpful feature in many circuits, including the present one as it enables a single supply rail to be used where a dual balanced supply would otherwise be needed. In many applications the negative supply is needed simply in order to permit the output of the op-amp to reach the 0volt rail. In applications of this type the CA3240E device normally enables the negative supply to be dispensed with.
As the CA3240E has a MOS input stage for each section the input impedance is very high (about 1.5 million Megohms!) and obviously no significant input current flows into the device. This, together with the high quality of the constant current source, and the practically non-existent distortion through IC1b due to the high feedback level gives this circuit excellent linearity.
With no resistor connected across T1 & T2 M1 will be taken beyond full-scale deflection and overloaded by about 100 or 200%. This is unlikely to damage the meter, but to be on the safe side a push-to-test on/off switch (S1) is used. Thus the power is only applied to the circuit when a test resistor is connected to the unit, and prolonged meter overloads are thus avoided.
A small (PP3 size) 9 volt battery is a suitable power source for this project which has a current consumption of around 5mA and does not require a stabilised supply.
Photos showing inside and outside of the completed Linear Resistance Meter.



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Oscilloscope testing module (huntron circuit)


Circuit diagram

I call this the "huntron circuit" because a company by that name made a similar device. It is useful for trouble-shooting. I used it with digital PC boards where I did not have a schematic, or even know how it worked. I recorded the patterns found on a good board and compared them with the patterns from a defective board. Any low power 12 volt transformer will work, the resistors are ? watt.

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Sunday, June 24, 2012

Telephone line monitor

Telephone Recorder
This nifty little circuit lets you record your phone conversations automatically. The device connects to the phone line, your tape recorder's microphone input, and the recorder's remote control jack. It senses the voltage in the phone line and begins recording when the line drops to 5 volts or less.
Circuit diagram

Parts
R1 270K 1/4 W Resistor
R2 1.5K 1/4 W Resistor
R3 68K 1/4 W Resistor
R4 33K 1/4 W Resistor
C1 0.22uF 150 Volt Capacitor
Q1, Q2 2N4954 NPN Transistor
D1 1N645 Diode
MISC Wire, Plugs To Match Jacks On Recorder, Board, Phone Plug
Notes
1. The circuit can be placed anywhere on the phone line, even inside a phone.
2. Some countries or states require you to notify anyone you are talking to that the conversation is being recorded. Most recoders do this with a beep-beep. Also, you may have to get permission from the phone company before you connect anything to their lines.

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Telephone amplifier

Circuit diagram

While talking to a distant subscriber on telephone, quite often we feel frustrated when the voice of the distant subscriber is so faint that it is barely intelligible. To overcome the problem, circuit of an inexpensive amplifier is presented here. It can be assembled and tested easily. There is no extra power source needed to power up the circuit, as it draws power from the telephone line itself. The amplifier will provide fairly good volume for the telephone conversation to be properly heard in a living room. A volume control is included to adjust the volume as desired.
The circuit is built around IC LM386. Diodes D6 and D7 are used to limit the input signal strength. Transformer X1 is a transistor radio's output transformer used in reverse. As original secondary (output) winding is connected in series with the telephone lines, the speech signals passing through the lines cause change in the magnetic flux in the core of transformer and thereby induce signal voltage across the primary winding. This audio signal is used as input for IC LM386. Diodes D2 through D5 connected in bridge configuration constitute a polarity guard so that the amplifier is powered with correct polarity, irrespective of the line polarity, Zener diode D1 may have any breakdown voltage between 6 and 12 volts range. e.
There is no need of a separate power switch as the circuit energises (via the normally open contacts of the cradle switch) when one lifts the handset.
The circuit may be wired on a general-purpose PCB or by etching a PCB for this circuit.
The circuit can be easily tested by connecting a 6 volts supply to line terminals 1 and 2. A hissing sound will be heard from the loudspeaker. Now connect 6V AC from a transformer to terminals 1 and 2 and observe hum in the loudspeaker. The volume of the hum can be changed through potentiometer VR1. Diodes D6 and D7 limit the input below ? 700 mV.
The circuit is to be connected to the telephone lines in series with the telephone instrument, as shown in the figure


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Telephone Hold Button

Although a hold feature is standard on most new phones, a lot of us still use the origional bell phones. Those of us that require a hold feature will find this circuit very useful. It is easy to build, and is compact enough to be installed inside the phone with no real problem. It is also powered by the phone line itself, eliminating the need for batteries.
Circuit diagram

Parts
R1 1.5K 1/4 W Resistor
R2 1K 1/4W Resistor
D1 1N4002 Silicon Diode or 1N4003, 1N4004, 1N4005, 1N4006, 1N4007
SCR1 C106Y SCR
LED1 Red LED or Green LED, Yellow LED
S1 Normally Open Push-Button Switch
MISC Wire, Board, Case (If Used)
Notes
1. To place a call on hold, simply hold down the button while hanging up the phone. To take a call off hold, just pick up the phone, or any extension.
2. Even though this is a simple circuit, you may have to check with your phone company before use.

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Wednesday, June 20, 2012

24 Hour Timer

Description:
These two circuits are multi-range timers offering periods of up to 24 hours and beyond. Both are essentially the same. The main difference is that when the time runs out, Version 1 energizes the relay and Version 2 de-energizes it. The first uses less power while the timer is running; and the second uses less power after the timer stops. Pick the one that best suits your application.

Notes:
The Cmos 4060 is a 14 bit binary counter with a built in oscillator. The oscillator consists of the two inverters connected to Pins 9, 10 & 11; and its frequency is set by R3, R4 & C3.The green Led flashes while the oscillator is running: and the IC counts the number of oscillations. Although it's a 14 bit counter, not all of the bits are accessible. Those that can be reached are shown on the drawing.
By adjusting the frequency of the oscillator you can set the length of time it takes for any given output to go high. This output then switches the transistor; which in turn operates the relay. At the same time, D1 stops the count by disabling the oscillator. Ideally C3 should be non-polarized; but a regular electrolytic will work, provided it doesn't leak too badly in the reverse direction. Alternatively, you can simulate a non-polarized 10uF capacitor by connecting two 22uF capacitors back to back (as shown).
Using "Trial and Error" to set a long time period would be very tedious. A better solution is to use the Setup tables provided; and calculate the time required for Pin 7 to go high. The Setup tables on both schematics are interchangeable. They're just two different ways of expressing the same equation.
For example, if you want a period of 9 Hours, the Range table shows that you can use the output at Pin 2. You need Pin 2 to go high after 9 x 60 x 60 = 32 400 seconds. The Setup table tells you to divide this by 512; giving about 63 seconds. Adjust R4 so that the Yellow LED lights 63 seconds after power is applied. This will give an output at Pin 2 after about 9 Hours.
The Support Material for the timers includes a detailed circuit description - parts lists - a step-by-step guide to construction - and more. A suitable Veroboard layout for each version is shown below:

The timer was designed for a 12-volt supply. However, provided a suitable relay is used, the circuit will work at anything from 5 to 15-volts. Applying power starts the timer. It can be reset at any time by a brief interruption of the power supply. The reset button is optional; but it should NOT be used during setup. The time it takes for the Yellow LED to light MUST be measured from the moment power is applied. Although R1, R2 and the two LEDs help with the setup, they are not necessary to the operation of the timer. If you want to reduce the power consumption, disconnect them once you've completed the setup. If you need a longer period than 24-hours, increase the value of C3.

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Asymmetric Timer

Description:
A timer circuit with independent mark and space periods.
Circuit diagram

Notes:
A simple astable timer made with the 555, the mark (on) and space (off) values may be set independently. The timing chain consists of resistors Ra, Rb and capacitor Ct. The capacitor, Ct charges via Ra which is in series with the 1N4148 diode. The discharge path is via Rb into into pin 7 of the IC. Both halves of the timing period can now be set independently.
The charge time (output high) is calculated by:
T(on) = 0.7 Ra Ct
The discharge time (output low) is calculated by:
T(off) = 0.7 Rb Ct
Please note that the formula for T(on) ignores the series resistance and forward voltage of the 1N4148 and is therefore approximate, but T(off) is not affected by D1 and is therefore precise.

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Repeating Interval Timer

Description:
This circuit has an adjustable output timer that will re-trigger at regular intervals. The output period can be anything from a fraction of a second to half-an-hour or more - and it can be made to recur at regular intervals of anything from seconds to days and beyond.
Circuit diagram

The Output Section:
The output section is a simple Monostable Circuit. When Pin 6 of the Cmos 4001 is taken high - the monostable triggers - and the relay energizes. It will remain energized for a period of time set by C1 & R3.
With the values shown - R3 will provide output periods of up to about 30-minutes. However, you can choose component values to suit your requirements. For example, if you reduce R3 to 1meg - and C1 to 4.7uF - the maximum output period is between 3 and 5 seconds. Owing to manufacturing tolerances - the precise length of the time period available depend on the characteristics of the actual components you've used.
The Cmos 4060:
The Cmos 4060 is a 14-bit binary counter with a built-in oscillator. The oscillator consists of the two inverters connected to Pins 9, 10 & 11 - and its frequency is controlled by R7. The output from the oscillator is connected internally to the binary counter. While the oscillator is running - the IC counts the number of oscillations - and the state of the count is reflected in the output pins.
By adjusting R7 - you can set the length of time it takes for any given output pin to go high. Connect that output to Pin 6 of the Cmos 4001 and - every time it goes high - it'll trigger the monostable.
Ideally C4 should be non-polarized - but a regular electrolytic will work - provided it doesn't leak too badly in the reverse direction. Alternatively - you can simulate a non-polarized 10uF capacitor by connecting two 22uF capacitors back to back - as shown.
Veroboard Layout:

Since the delays between outputs can last for hours - or even days - using "Trial and Error" to set-up the timer would be very tedious. A better solution is to use the Setup Table provided - and calculate the time required for Pin 7 of the Cmos 4060 to go high.
For example, if you want the monostable to trigger every Six Hours - the Range Table tells you to use Pin 1 of the Cmos 4060. You need Pin 1 to go high every 6 x 60 x 60 = 21 600 seconds. The Setup table tells you that for Pin 1 you should divide this figure by 512 - giving about 42 seconds. Adjust R7 so that the Yellow LED lights 42 seconds after power is applied. This will cause Pin 1 to go high after about 3 Hours.
Setup Tables:

When Pin 1 goes high it will stay high for three hours. It will then go low for three hours - before going high once again. Thus, Pin 1 goes high once every six hours. It's the act of going high that triggers the monostable. So - after an initial delay of three hours - the relay will energize. It will then re-energize every six hours thereafter.
The reset button should NOT be used during setup. The time it takes for Pin 7 to go high - and the Yellow LED to light - MUST be measured from the moment power is applied.
Although R4, R5 and the two LEDs help with the setup - they are not necessary to the operation of the timer. If you want to reduce the power consumption - disconnect them once you've completed the setup.
The timer is designed for a 12-volt supply. However - provided a suitable relay is used - it will work at anything from 5 to 15-volts. Applying power starts the timer. It can be reset at any time by a brief interruption of the power supply - so a reset button is not strictly necessary. If you need delays in excess of 32-hours - increase the value of C4.
The Support Material for this circuit includes a step-by-step guide to the construction of the circuit-board - a parts list - a detailed circuit description - and more.


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Tuesday, June 19, 2012

Jogging Timer

3V Battery powered
Beeps after a fixed number of minutes
Circuit diagram
http://www.hqew.net/circuit-diagram/Jogging-Timer_5031.html
Parts:
R1 47K 1/4W Resistor
R2 10M 1/4W Resistor
R3 1M 1/4W Resistor
R4 12K 1/4W Resistor (see notes)
C1,C3 10?F 25V Electrolytic Capacitors
C2 100nF 63V Polyester Capacitor
D1 1N4148 75V 150mA Diode
IC1 4093 Quad 2 input Schmitt NAND Gate IC
IC2 4060 14 stage ripple counter and oscillator IC
IC3 4017 Decade counter with 10 decoded outputs IC
Q1 BC337 45V 800mA NPN Transistor
SW1 1 pole 9 ways Rotary Switch (see notes)
SW2 SPST Slider Switch
BZ1 Piezo sounder (incorporating 3KHz oscillator)
B1 3V Battery (two 1.5V AA or AAA cells in series etc.)
Device purpose:
This circuit was developed since a number of visitors of this website requested a timer capable of emitting a beep after one, two, three minutes and so on, for jogging purposes.
As shown in the Circuit diagram, SW1 is a 1 pole 9 ways Rotary Switch. Setting the switch in position 1, the Piezo sounder emits three short beeps every minute. In position 2 the same thing happens after 2 minutes, and so on, reaching a maximum interval of 9 minutes in position 9.
Notes:
Needing only one time set, rotary switch can be replaced by an hard-wired link.
A DIP-Switch can be used in place of the rotary type. Pay attention to use only a switch at a time, or the device could be damaged.
Varying R4 from 10K to 15K you can obtain more or less than three short beeps after the preset time delay.
To obtain a one-second beep only, after the preset time delay, disconnect pin 9 of IC1C from pin 9 of IC2 and connect it to pin 8 of IC1C.

Tan Timer

Six timing positions suited to different skin types
Timing affected by sunlight intensity
Circuit diagram

Parts:
R1 47K 1/4W Resistor
R2 1M 1/4W Resistor
R3,R5 120K 1/4W Resistors
R4 Photo resistor (any type)
C1,C3 10?F 25V Electrolytic Capacitors
C2 220nF 63V Polyester Capacitor
D1,D2 1N4148 75V 150mA Diodes
IC1 4060 14 stage ripple counter and oscillator IC
IC2 4017 Decade counter with 10 decoded outputs IC
Q1 BC337 45V 800mA NPN Transistor
SW1 2 poles 6 ways Rotary Switch (see notes)
SW2 SPST Slider Switch
BZ1 Piezo sounder (incorporating 3KHz oscillator)
B1 3V Battery (two 1.5V AA or AAA cells in series etc.)
Device purpose:
This timer was deliberately designed for people wanting to get tanned but at the same time wishing to avoid an excessive exposure to sunlight.
A Rotary Switch sets the timer according to six classified Photo-types (see table).
A Photo resistor extends the preset time value according to sunlight brightness (see table).
When preset time ends, the beeper emits an intermittent signal and, to stop it, a complete switch-off of the circuit via SW2 is necessary.

Photo-type, Features and Exposure time

I & childrenLight-eyed, red-haired, light complexion, freckly 20 to 33 minutes
IILight-eyed, fair-haired, light complexion 28 to 47 minutes
IIILight or brown-eyed, fair or brown-haired, light or slightly dark complexion 40 to 67 minutes
IVDark-eyed, brown-haired, dark complexion 52 to 87 minutes
VDark-eyed, dark-haired, olive complexion 88 to 147 minutes
VIThe darkest of all 136 to 227 minutes
Note that pregnant women belong to Photo-type I
Notes:
Needing only one time set suitable for your own skin type, the rotary switch can be replaced by hard-wired links.
A DIP-Switch can be used in place of the rotary type. Pay attention to use only a switch at a time when the device is off, or the ICs could be damaged.

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Digital Stopwatch 0-99sec

Introduction
In the present article, we will describe the function of a digital stopwatch, 0 ? 99 sec. The function of the stopwatch, relies in the use of 4 integrated circuits, which in this case belong to National Semiconductor (http://www.national.com). It is obvious that other integrated circuits can be used to achieve the same result, however in this case we have used the following parts:
Α. 1 x CD4060BM (14 stage ripple carry binary counter)
B. 1 x CD4040BM (14 stage ripple carry binary counter)
C. 1 x MC14518B (BCD counter)
D. 2 x MC14511B (BCD to seven segment driver)
E. 2 x 7 segment LED displays
The circuit that has been used is shown in picture 1. Through the experimental part we will explain each of the parts function, but in order to have a notion of the basic idea, let just say, that this circuit besides the 5V power supply, is fed with a pulse which comes from a crystal. The crystal?s pulse is devided properly in order to obtain the 1 Hz pulse which we need in order for the circuit to work properly, and display the seconds on the 7 segment displays, through a procedure which we will explain through the experimental part.
Circuit diagram
http://www.hqew.net/circuit-diagram/Digital-Stopwatch-0$2d99sec_5027.html
Description
We will begin the description of the digital circuit above. For our convenience we will devide the circuit to 2 parts: the generator, which produces the pulse of the desired frequency, and the part that does the actual counting.
Generator:
The generator of the circuit comprises of the integrated circuits CD4040CM and CD4060CM. We use a crystal which oscillates at a frequency of 4,194,304MHz. It is obvious that this frequency is completely useless, as it is too big to be used as it is to our circuit. What we should is devide this frequency, in a way that in its final form, the pulse will have a frequency of 1Hz, which is the desirable frequency. Initially we use the integrated CD4060, which devides the imported frequency in its input, by forces of 2. As we can see on the integrated circuit the outputs are marked as Q4, Q5,? Qn. By importing a pulse in the CLK input of the 4060, with a frequency f Hz, we take out of output Qn, a signal which has a frequency equal to f/2n,. So, by exporting the signal out of Q14, knowing that the imported signal has a frequency of 4,194,304Hz, we take a signal, which has a frequency of 256Hz.
By importing this signal, to 4040 and by exporting the signal through Q8 we have finally taken an inverted signal, at the frequency of 1Hz. The fact that the signal is inverted, firstly doesn?t affect the proper function of our circuit and secondly is due to the inversion of the CLK input as we can see. This inversion just causes, the following circuit to be triggered with a logical ?0?. By putting a LED on the same output, we have a visual of the counting, as in each positive pulse the diode polarizes positively, and a current passes through it.
Counter:
The signal of 1Hz, which we have taken from the generator, is imported to a BCD counter MC14518. This integrated circuit adds a logical ?1? at each pulse, on its output.του. .The MC14518 is virtually divided into two segment. One counts the units of the seconds, while the other the decades. As we can see in picture 1, the generators pulse is imported to the part which counts the units. This is very logical, as we want in each secont the number of the display to be raised by 1. On the other hand, we want the first display to raise by 1, every 10 seconds. This is why, we ground the CLK input, and we use the signal of Q3 to the CKE input.
By using this means, we make sure that the first display will be triggered, only when we have a decreasing signal on Q3; that is, only when the signal drops from logical ?1? to logical ?0?. As we can see, the first display increments every 10 seconds, which means that after 9 on the second display (1001 on the output of the BCD counter) the first display must be set to zero, while the first must be set to 1. That is that from 1001 ? 0000, and we have a descending pulse, as the last digit descends from logical ?1? to logical ?0? and triggers the BCD counter of the decades. When the decades display becomes 9 then the circuit goes to the next state, which is zero, and the counting begins once more.

The integrated circuits MC14511 are BCD to 7 segment drivers. As its name clearly state, their sole purpose is to translate the BCD information of MC14518, to a code understandable by the 7 segment displays. The inputs (Lamp Test, Blanking) are used to test the LEDs of the display and pulse modulate the brightness of the display. In this case we these inputs to logical ?0?, as we don?t need them. The LE input (Latch Enable) is used to keep the number of the displays while the pulse still runs. It is a HOLD function similar to the one of the modern stopwatches.
In addition, at any given moment we can restart the counting, by pressing the reset switch. By this means we set the RST input of the MC14518 to logical ?1?, which resets the counting to 0000.

Source: http://www.hqew.net/circuit-diagram/Digital-Stopwatch-0$2d99sec_5027.html

Monday, June 18, 2012

iPad 2 Drives Global Tablet PC Price to a Reduction of 21% in the First Quarter

The market research firm IMS Research, reported the global average price of the Tablet PC  in the first quarter of this year was $386, down 21%, and the main stimulus factor was Apple lowered the iPad 2 price.

Apple released the new iPad in March this year and subsequently the iPad 2 price was reduced $100 to $399, which leaded to the other Tablet PC manufacturers being forced to lower product price, and it became the main reason that the Tablet PC average selling price was only $ 386 in the first quarter.

In fact, with the growth in demand, low-end tablet PCs below $200 became more common. Although the world's Tablet PC shipments was less than the fourth quarter of last year in the first quarter this year, it double increased compared to the first quarter of last year.

IMS Research analyst Gerry Xu said:" Manufacturers need have small innovation to differentiate their tablet computer products, low price seems to be the greatest incentive to attract consumers to buy the Tablet PC besides  iPad. But to balance performance and profitability, cutting price is still a challenge for most of the Tablet PC manufacturers."

The survey shows that the low-end market is currently occupied by small and medium-sized brands and cottage manufacturers, users of these companies use Tablet PC as a media player, eBook reader and GPS. But the new version of Amazon Kindle Fire Tablet PC is expected to pressure the low-end market manufacturers, prompt the latter to improve product performance. Kindle Fire is now America's most popular Android tablet computer.

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Sleeping-Aid

Based on electromagnetic-field radiation
Place it under the pillow - Built-in timer
Circuit diagram

Parts:
R1,R5 1K 1/4W Resistors
R2 10K 1/4W Resistor
R3,R6 10M 1/4W Resistors
R4,R7 2M2 1/4W Resistors
R8,R9 4K7 1/4W Resistors
C1,C7 47?F 25V Electrolytic Capacitors
C2 100nF 63V Polyester Capacitor
C3,C4 330nF 63V Polyester Capacitors
C5,C6 15nF 63V Polyester Capacitors
D1,D3,D4,D5 1N4148 75V 150mA Diodes
D2 LED (any type) (see Notes)
IC1 4060 14 stage ripple counter and oscillator IC
IC2 4093 Quad 2 input Schmitt NAND Gate IC
Q1 BC327 45V 800mA PNP Transistor
L1 Radiator coil (see Notes)
P1 SPST Pushbutton
SW1 2 poles 4 ways rotary switch
SW2 SPST Slider Switch
B1 9V PP3 Battery
Clip for PP3 Battery
Features:
Generates a natural electromagnetic-field
Makes easier to fall asleep
nduces a prolonged and sound sleep without drugs
No side effects
Device purpose:
Many people experienced sleeping well in natural surroundings, into a tent or a wooden hut. This fact is due not only to the healthy atmosphere but also from our unconscious ability to perceive natural Earth's magnetic-fields.
The circuit generates this type of Geo-magnetic-fields and lets us perceive them: in this manner our brain is surrounded by an ideal environment for a sound sleep.
(N.B. Basic ideas for this circuit are coming from German papers).
Use:
Select a timing option by means of the rotary switch SW1.
Choose 15, 30 or 60 minutes operation.
Select "Stop" or "Alternate" mode operation by means of SW2.
With SW2 closed (Stop mode operation) the electromagnetic radiation stops after the pre-set time is elapsed.
With SW2 opened (Alternate mode operation) the device operates for the pre-set time, then pauses for the same amount of time: this cycle repeats indefinitely.
Place the unit under the pillow and sleep like a log.
To reset a cycle press P1 pushbutton.
Circuit operation:
IC2C and IC2D generate two square waves at about 1.2 and 5 Hz respectively. These wave-forms are converted into 60?S pulses at the same frequencies by means of C5 & C6 and mixed at Q1's Base. This transistor drives the Radiator coil with a scalar series of pulses of 60?S length and 9V amplitude.
IC1, IC2A & IC2B form the timer section. C1 & R2 provide auto-reset of IC1 at switch-on. The internal oscillator of IC1 drives the 14 stage ripple counter and, after about 15 minutes, output pin 1 goes high. Pin 3 of IC2A goes low and stops IC2C & IC2D oscillation.
If SW2 is left open (Alternate mode operation), after 15 minutes pin 1 of IC1 goes low, pin 3 of IC2A goes high and oscillators are enabled again.
If SW2 is closed (Stop mode operation), the first time output pin 1 of IC1 goes high, the internal oscillator of the IC is disabled by means of D1. Therefore the circuit remains off until a reset pulse is applied to pin 12 by means of P1 or when the whole device is switched-off and then restarted.
The same thing occurs when SW1 is switched on 30 or 60 minutes positions, obviously changing time length.
IC2B drives pilot LED D2 which operates in the following three modes:
flashes quickly and almost randomly when the Radiator coil is driven
flashes somewhat slowly and regularly when the Radiator coil is pausing during the Alternate mode operation
is off when the circuit auto-stops (Stop mode operation)
Notes:
L1 is obtained by winding randomly 600 turns of 0.2 mm. enameled wire on a 6 mm. diameter, 40 mm. long, steel bolt. Secure the winding with insulating tape.
Mean current drawing is about 7mA, decreasing to less than 4mA during pauses when in Alternate mode operation.
Battery life can be dramatically increased omitting LED D2 and its associated resistor R5.
Use a plastic box to enclose the circuit: metal cases can severely limit electromagnetic radiation.

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Cuckoo sound Generator

Agreeable, very close sound imitation
Suitable for sound effects, door-bells etc.
Circuit diagram

Parts:
R1,R5 1K 1/4W Resistors
R2 50K 1/2W Trimmer Cermet
R3 8K2 1/4W Resistor
R4 82K 1/4W Resistor
R6 1M 1/4W Resistor
R7,R17,R20,R21 22K 1/4W Resistors
R8,R10,R11,R19 10K 1/4W Resistors
R9 150K 1/4W Resistor
R12 4K7 1/4W Resistor
R13 100K 1/4W Resistor
R14 220R 1/4W Resistor
R15,R22 20K 1/2W Trimmers Cermet
R16 10R 1/4W Resistor
R18 200K 1/2W Trimmer Cermet
C1,C11 47nF 63V Polyester or Ceramic Capacitors
C2,C10,C12 220?F 25V Electrolytic Capacitors
C3 220nF 63V Polyester or Ceramic Capacitor
C4 22nF 63V Polyester or Ceramic Capacitor
C5,C6,C8,C9 100nF 63V Polyester or Ceramic Capacitors
C7,C13,C14 10?F 63V Electrolytic Capacitors
D1,D2,D3,D6__1N4148 75V 150mA Diodes
D4,D5 BAT46 100V 150mA Schottky-barrier Diodes
Q1,Q2 BC547 45V 100mA NPN Transistors
IC1 7555 or TS555CN CMos Timer IC
IC2 4093 Quad 2 input Schmitt NAND Gate IC
IC3 4017 Decade counter with 10 decoded outputs IC
IC4 LM386 Audio power amplifier IC
P1 SPST Pushbutton
SW1 SPST Switch
SPKR 8 Ohm Loudspeaker
Comments:
This circuit generates a two-tone effect very much alike the cuckoo sound. It can be used for door-bells or other purposes thanks to a built-in audio amplifier and loudspeaker
Used as a sound effect generator it can be connected to external amplifiers, tape recorders etc. In this case, the built-in audio amplifier and loudspeaker may be omitted and the output taken from C8 and ground.
There are two options: free running, when SW1 is left open, and one-shot, when SW1 is closed. In this case a two-tone cuckoo sound will be generated each time P1 pushbutton is pressed.
Circuit operation:
IC1 is wired as a squarewave generator and produces both tones of the cuckoo sound. The frequency of the higher one (667Hz) is set by means of Trimmer R2. When IC2D output goes low, a further Trimmer (R22) is added to IC1 timing components via D6, and the lower tone (545Hz) is generated.
To imitate closely the cuckoo sound, the squarewave output of IC1 is converted to a quasi-sinusoidal waveform by R3, R4, C3 and C4, then mixed with the white noise generated by Q1, R6.
Q2 has two purposes: it mixes the two incoming signals and gates the resulting tone, shaping its attack and decay behavior by means of the parts wired around its Emitter.
IC4 is the audio power amplifier driving the speaker and R15 is the volume control.
The various sound and pause timings for the circuit are provided by the clock generator IC2A driving the decade counter IC3. Some output pins of this IC are gated by IC2C, IC2D and related components to drive appropriately the sound generator and the sound gate.
When SW1 is left open the circuit operates in the free-running mode and a cuckoo sound is generated continuously. When SW1 is closed, the circuit generates two tones then stops, because a high state appears at the last output pin (#11) of the decade counter IC: therefore the count is inhibited by means of D1 feeding pin #13.
The circuit is reset by a positive pulse at pin #15 of IC3 when P1 is pressed.
Setup:
Best results will be obtained if the two tones frequencies are set precisely, i.e. 667Hz for the first tone and 545Hz for the second: in musical terms this interval is called a Minor Third. Obviously a digital frequency counter, if available, would be the best tool to setup R2 and R22, but you can use a musical instrument, e.g. a piano or guitar, tuning-up the notes accurately by ear.
Disconnect temporarily R22 from D6 anode
Connect the digital frequency counter to pin 3 of IC1
Adjust R2 in order to read 667Hz on the display
Connect R22 to negative ground and adjust it to read 545Hz on the display
Restore R22 - D6 connection
Tuning by ear:
Disconnect temporarily R22 from D6 anode
Disconnect C8 from Q2 Collector and connect it to R4, C4 and C5 junction
Adjust R2 in order that the tone generated by the loudspeaker is at the same pitch of the reference note generated by your musical instrument. This reference note will be the E written on the stave in the fourth space when using the treble clef
Connect R22 to negative ground and adjust it in order that the tone generated by the loudspeaker is at the same pitch of the reference note generated by your musical instrument. This second reference note will be the C-sharp written on the stave in the third space when using the treble clef
Restore R22 - D6 and C8 to Q2 Collector connections
Notes:
The master clock can be adjusted by means of R18.
The percentage of hiss and sound in the mixing circuit, setting the tone character, can be varied changing R8 and R7 values respectively.
Any kind of dc voltage supply in the 12 - 15V range can be used, but please note that supply voltages below 12V will prevent operation of the white noise generator.
An amusing application of this circuit is to use a photo-resistor in place of P1, then placing the unit near the flashing lamps of your Christmas tree. A sweet cuckoo sound will be heard each time the lamp chosen will illuminate.

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Sunday, June 17, 2012

DC Motor Controller using Transistor TIP31 circuit diagram

DC Motor Controller using Transistor TIP31 circuit
This is a DC motor controller circuit, built using transistor TIP31 based on H-Bridge concept. The switch S1 and S2 are normally open , push to close, press button switches. The LED function is to indicate the direction of motor rotation, you may use any common LED type. The TIP31 transistors capable to handle 3A maximum electric current, you may change the transistors for DC motors with higher current consumption. Remember, running under load draws more current.
Actually, this circuit was built to drive a small DC motor and can be used for small application such as automatic closing and opening systems, mobile robot actuator, small fan, etc. The four diodes arround the DC motor are back EMF diodes. The diode type is depended of the DC motor current consumption. For a 12V motor drawing 1A under load, use 1N4001 diodes. For 3A DC motor, then use IN5401.

Simple Metal Detector circuit diagram

Simple Metal Detector circuit
This is a very simple and easy build metal detector circuit, built based on a CS209A IC. The circuit will give surprising results and draws extremely small current from a 9 volt battery.
It worked great on the Bench, But not so good outside for common metal detecting. But Definately a great circuit for sensing studs in a wall, using the proper coil!
This certain circuit was built so it could be implemented with an LED and Buzzer or only the LED or only the Buzzer. Battery voltage could be up to 20 volts, however it does not add to the sensitivity.
Additionally, Modifications to the Potentiometer value could be created, adding a smaller pot in series to create a extra sensitive trip point.
This circuit operates on the principal of adjustments in “Q” of the coil. So it’s crucial to attempt and make a High Q coil! But I discovered that even very simple coils gave fairly effective results! It’s suggested to work with “Litz” Wire, But I just applied vinal covered wire on 1 and also yet another with magnet wire and I got quite good results with both coils. Having now put a board together along with a couple of tests outside, it appears the coil requires a Faraday Shield.

Electro Harmonix Fuzz-Wah Guitar Effect circuit diagram

Electro Harmonix Fuzz Wah Guitar Effect circuit
This is the electro harmonix fuzz-wah guitar effect pedal circuit diagram.
Circuit Notes:
  • Q1 & Q2 are 2n3565
  • Fuzz bypass S1 has been improved to provide true bypass
  • S3 chooses volume or wah-wah
  • S5 provides for sweep reverse
  • S2 gives just fuzz, just wah-wah / volume, or fuzz into wah-wah / volume
  • S4 sets tone of filter
  • D1 & D2 can be any signal diode
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Thursday, June 14, 2012

400W Power Amplifier "Safari" circuit diagram

This 400W power amplifier circuit often called as “safari” amplifier.
400W Power Amplifier Safari circuit
The 400W power amplifier built using two couples of power transistors that are TIP31 with TIP32 and 2N3055 with MJ2955. These transistors are well known and widely used for the amplifier circuit and power supply circuit.
Take a note that you must use aluminium heatsink (and a fan) to prevent over heating on the transistor (2N3055/MJ2955). This circuit require dual polarity power supply. You may use this dual polarity power supply circuit. Use 5A center tapped amplifier with voltage output of 25V-0-25V or 32V-0-32V. The capacitor type is electrolytic capacitor, recommended value: 4 x 6800uF/63V (minimum). 10000uF will be better.
 

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4 Transistors FM Transmitter circuit diagram

The following diagram is the schematic diagram of 4 transistors FM transmitter circuit designed by Paul K. Sherby.
4 Transistors FM Transmitter circuit
Components List:
R1,R2,R8 = 1K
R3 = 100K
R4 = 150K
R5,R7 = 10K
R6 = 220 ohm
R9 = 10 ohm
P1 = 5K trimpot
D1 = 1N4002
Q1,Q2 = 2N3904
Q3,Q4 = 7001, NTE123AP
C1 = 1uF/63V
C2,C3 = 10nF
C4,C5,C9 = 4.7uF/63V
C6,C12,C13,C14 = 1nF
C7,C8,C11 = 5pF
C10 = 220uF/63V
L1 = 3.9uH
L2 = 1uH
L3 = aircoil, 8.5 turns air space, 1/4 inch diameter
Circuit Notes:
This circuit delivers an FM modulated signal having an output power of about 500mW. The input microphone pre-amplifier is designed close to a pair of 2N3904 transistors (Q1/Q2), and audio gain is restricted by the 5k preset trimmer potensiometer (trimpot).
The oscillator is actually a Colpitts stage, frequency of oscillation governed by the tank circuit built from two 5pF ceramic capacitors along with the L2 inductor. Frequency is about 100Mhz with values shown.
Audio modulation is fed in to the tank circuit via the 5p capacitor, the 10k resistor and 1N4002 controlling the quantity of modulation. The oscillator output is fed in to the 3.9uH inductor (L1) which will have a high impedance at RF frequencies.
The output stage operates as a ‘Class D’ amplifier, no direct bias is applied but the RF signal developed across the 3.9uH inductor is enough to drive this stage. The emitter resistor and 1k base resistor avoid instability and thermal runaway in this stage.
Some substitutes for the2N3904are: NTE123AP, 2N4401, BC547 (watch lead orientation), and so on. The 7001 (Q2/Q3) oddly enough also reference towards the NTE123AP. Even though the 2N3904 is really common and effortlessly available.
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Current Output Multiplier for 78xx Regulator circuit diagram

By default, the regulator ID 78xx series will give maximum current output 1A – 1.5A. To increase the current output of this regulator, you may consider this circuit.
Current Output Multiplier for 78xx Regulator circuit
Parts list:
R1, R2 = 4.7 K
C1, C2 = 4700 uF / 16V
C3 = 47,000 uF / 35V
D1,D2, D3 = 1N5401 ( 3 Amp Diodes )
D4 & D5 – Light Emitting Diodes (LED)**
IC1, IC2 – 78xx series regulator IC ( 7805 for 5V, 7812 for 12V etc.)
Detail instruction: go to this page
My Notes:
  • The original circuit source said that the diode is1N4003(3A diodes). That’s is a mistake, the correct diodes should be1N5401
  • Schottky diodes is recommended
 

Wednesday, June 13, 2012

Alternating Relay Switch

Our reader Andrea (andrea[dot]perugia[-at-]gmail[dot] com) sent his circuit to us, and he creates the circuit for educational intent. The main purpose is to show that you can toggle an output state electronically, although physically you use only a push button switch. Here is what he said about the cicuit :
This simple circuit can be utilized to drive a monostable relay, using a single button switch. When I press the button IC output (pin 3) assumes the high level, but Q1 transistor switches off. So when I release the button the relay is energized (now the exchange switch is closed on 5 and 9). When I press the button again IC output assumes the low level, but Q3 transistor switches on:
when I release the button the circuit goes to the start condition.
Here is the schematic diagram of the circuit:
alternating relay switch circuit schematic



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RJ45 Port Pinout

RJ45 is used to connect Ethernet port on your computer. There are two configuration: straight and cross. Straight RJ45 cables should be used to connect between computer and device such as switch or hub, and cross RJ45 cables should be used in computer-to-computer connection. Some hub or switch has the capability to detect the cable type and accept both straight and cross RJ45 cables. Here is the RJ45 pin and wiring diagram:

rj45 port pinout diagram circuit schematic
A straight Ethernet cable has same RJ-45 pin-out configuration at both end of the CAT-5 cable, either by using EIA/TIA-568A standard or EIA/TIA-568B standard.


Source: http://www.hqew.net/circuit-diagram/RJ45-Port-Pinout_3991.html

RS232 (COM) Port Pinout Diagram

This pin diagram will be useful when viewing these connectors. Sometimes you hold asoldering ironto the back of the connector, and you don’t remember the numbering of the pin. Here is the pin diagram for your reference:

rs232 com pinout circuit schematic
The number of each pins are actually stamped on both sides of any D-type connector. Unfortunately, since they are only moldings, they are very difficult to see as they have no color difference.



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Tuesday, June 12, 2012

Compact Power Factor Controller


This is compact power factor controller circuit. It stabilizes device’s electrical demand to give best power factor characteristic of many types of loads. In many application, a direct rectification of the AC line followed by bulk capacitor filtering is used to get the high DC voltage. This capacitor filtering will produce a poor power factor and current spike that distort the power line sine waveform and resulting in? the real power that is much lower than an apparent input power. To? solve this problem, we can insert a pre-regulation between the bulk capacitor and the rectifier. Here is the circuit:
compact power factor controller1 circuit schematic diagram
This power factor controller uses IEC1000–3–2 standard that is a low–cost system solution for boost mode follower. It includes protection against undervoltage, overvoltage, overcurrent, and an inrush current detection. Smaller inductor and MOSFET can be used for follower boost mode to reduce system cost. [Circuit schematic source: http://www.hqew.net/circuit-diagram/Compact-Power-Factor-Controller_3972.html]

BQ24105 Switch Mode Lead Acid Battery Charger


Switch mode circuits can implement the lead acid battery charger with a more efficient. It can be constructed using bq24105 battery charger controller. The bq24105 was originally designed to charge single-, two- or three-cell Li-polymer and Li-ion battery packs. The bq24105 doesn’t has a feature? to control lead acid battery charger termination. So external circuitry is added? to enable this controller to charge lead acid batteries. Switching mode charging method for lead acid batteries provides high efficiency, although the circuit becomes more complex. Here is the circuit :
switching battery charger circuit schematic diagram
Lead-acid battery charging system design specification:
  • Input power source Vin: 17 ± 1 Vdc
  • Battery bulk voltage regulation: 14.8 V
  • Battery voltage Vbat: 12-V lead-acid battery
  • Battery refresh voltage: 13.6 V
  • Fast-charge current: 0.5 A for Vbat ? 13.5 V, 1 A for Vbat > 13.5 V
  • Precharge current: 0.45 A
  • Termination current: 0.9 A
[Schematic diagram source: http://www.hqew.net/circuit-diagram/BQ24105-Switch-Mode-Lead-Acid-Battery-Charger_3961.html]

Lead Acid Battery Charger Circuit

To charge lead-acid batteries we can use this circuit that consist of a current-limited power supply and a flyback converter topology. Here is the schematic diagram of the circuit :
lead acid battery charger circuit circuit schematic diagram
Isolation and voltage input range flexibility are provided by the flyback transformer, even at the battery voltage higher than supply voltage.MAX471current sense amplifier is used to monitor the charging current by sensing the output. To detect if the value falls below the predetermined threshold or not, this circuit uses the output current monitor’s result that gives a feedback to a threshold detector. When a lower voltage is applied for lower charging current, this circuit will switch the charger into trickle mode using the detection. [Circuit schematic source: http://www.hqew.net/circuit-diagram/Lead-Acid-Battery-Charger-Circuit_3971.html]

Monday, June 11, 2012

200mA/Hour – 12V NiCAD Battery Charger circuit diagram

The following diagram is the schematic diagram of 12V NiCAD battery charger with charging rate of 200mA/Hour.
200mA/Hour   12V NiCAD Battery Charger circuit
This NiCAD battery charger circuit charges the battery at 75 mA until the battery is charged, then it reduces the current to a trickle rate. It will fully recharge a dead/unpowered battery in 4 hours and the battery can be left in the charger indefinitely. To set the shut off point, connect a 270 ohm / 2 Watt resistor across the charge terminals and adjust the pot for 15.5V across the resistor.
 

Article from: http://www.hqew.net/circuit-diagram/200mA$2fHour-%E2%80%93-12V-NiCAD-Battery-Charger-circuit-diagram_3937.html

Tube Mic Pre-Amp circuit diagram

The following diagram is the circuit diagram of tube mic pre amplifier 12AX7. This circuit is little hard to built. You must have an intermediate or advanced skills to build this circuit.
Tube Mic Pre Amp circuit
All capacitors with value of 33uF are 16V, while the all others are 50V unless marked otherwise. Resistors marked with “#” are 1% metalfilm resistor type.

The “Drive” LED indicates how hard the tube is being driven. The “Blend” control allows for a mixing of SS and tube coloration. Symmetry controls the relative amounts of even and odd harmonics, CCW the Tube Mic Pre-Amp may sound punchier, while CW it may sound warmer. The 12VAC needed for pin 5 of the 12AX7 can be obtained from point G while pin 4 should be connected to point A.


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6A / 0-28V Variable Power Supply circuit diagram

The following diagram is the schematic diagram of variable power supply which will deliver 0 to 28V output voltage at 6/8 A electric current.
6A / 0 28V Variable Power Supply circuit
Component Part List:
R1 = 2K2 Ohm 2,5 Watt
R2 = 240 Ohm
R3,R4 = 0.1 Ohm 10 Watt
R7 = 6K8 Ohm
R8 = 10K Ohm
R9 = 47 Ohm 0.5 Watt
R10 = 8K2 Ohm
C1, C7, C9 = 47nF
C2 = 4700uF/50v – 6800uF/50v
C3, C5 = 10uF/50v
C4, C6 = 100nF
C8 = 330uF/50v
C10 = 1uF/16v
C11 = 22nF
D1…D4 = four MR750 (MR7510) diodes (MR750 = 6 Ampere diode) or 2 x 4 1N5401 (1N5408) diodes.
D5 = 1N4148, 1N4448, 1N4151
D6 = 1N4001
D10 = 1N5401
D11 = LED
D7, D8, D9 = 1N4001
TR = 2 x 15 volt (30volt total) 6 - Ampere
IC1 = LM317
T1, T2 = 2N3055
P1 = 5k
P2 = 47 Ohm or 220 Ohm 1 Watt
P3 = 10k trimmer
F1 = 1 Amp
F2 = 10 amp
Circuit Description:
This is an easy to make power supply that has reliable, clear and regulator 0 to 28 Volt 6/8 Amp output voltage. By making use of two 2N3055 transistor, you’ll get two times the amount of electric current.
Although the 7815 power regulator may kick in on short circuit, overload and thermal overheating, the fuses in the main section of the transformer and the fuse F2 at the output will safe your power supply. The rectified voltage of: 30 volt x SQR2 = 30 x 1.41 = 42.30 volt measured on C1. So all capacitors should be rated at 50 volts. Caution: 42 volt will be the voltage that could be on the output if 1 of the transistors ought to blow.
P1 lets you ‘regulate’ the output voltage to something in between 0 and 28 volts. The LM317 lowest voltage is 1.2 volt. To have a zero voltage on the output I’ve place 3 diodes D7,D8 and D9 around the output with the LM317 towards the base with the 2N3055 transistors. The LM317 optimum output voltage is 30 volts, but using the diodes D7,D8 & D9 the output voltage is approx 30v – (3x 0.6v) = 28.2volt.
Adjust your build-in voltmeter using P3 and, of course, a fine digital voltmeter is better solution.
P2 will let you to control the limit with the optimum available electric current in the output Vcc. When utilizing a 100 Ohm / 1 watt varistor the current is limited to approx. 3 Amps @ 47 Ohm and - 1 Amp @ 100 Ohms.
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